Check engine light just came on

The friendliest place on the web for anyone with an RV or an interest in RVing!
If you have answers, please help by responding to the unanswered posts.
See posts with no answers
I agree, and told Tom that last week. I only know about the AC voltage deal because mine did exactly the same thing last year coning home from the race track one night. When I had the alternator rebuilt my problems went away.The AC voltage will screw with the vss module, because that's what that part does. It converts AC voltage to reference dc voltage for the pcm.
 
I agree, the VSS is sensitive to A/C voltage as it works off an ac sine wave. If ac from the alternator would get through to the VSS it would give eroneous readings to the computer but the buffer is supposed to prevent that. Chevrolet will tolerate more ac ripple than most manufacturers. In the l80's Ford was losing ignition modules due to ac ripple. In this case, the 4l85E transmission has a computer which grounds the solenoids to get the shifts. It is normally a very reliable transmission with proper maintenance but has had some solenoid and shift valve problems when dirty and varnish get in the valve body. 
 
I  agree, but if the pcm thinks the inputs from the trans is not right, it will cause different things to happen. The trans is sent the command to shift or down shift from the inputs from the pcm. The pcm gets it's info on speed from the vss module, throttle position sensor, among others. This problem started all at once. If the inputs from the input and output speed sensor/generators don't jive the pcm will have a code. That code will be erased as soon as the key is switched off. That's why he doesn't get a hard code.

And if the alternator is putting out AC, his batteries won't like it much.
 
I drove two miles to the store this morning and that is the last time I will drive it until it is fixed. The condition is getting much worse. Up until now it ran fine when it was cold, but after 20 minutes of driving it started acting up. This morning it was acting up right from the start. It acted up all the way there and back.

It is definitely a loss of electrical power. I had not noticed until the last trip but the entire sequence of events starts with the volt meter dropping from 13.5 to 9 volts. Actually it is probably not even 9 volts, that is just the beginning of the scale on the meter. When the voltage drops the tranny shifts into neutral, the engine revs a bit, the gas gauge bounces and then it goes back to normal. Prior to today normal was about 90% of the time. Now normal is about 10%.

I had a guy who was going to come over and change the alternator but he never showed up. So now I have gotten a recommendation of a mobile RV mechanic from my insurance agent. I am waiting for him to call me. It sounds now like a loose connection, probably on the alternator. I am not nimble enough to look for loose wires, since the alternator is almost under the dash. So I will wait.
 
I agree Tom. They don't make these things so us old guys can work on them. My problem started with my alternator. When I was laying across the engine removing it, is when I bent the throttle linkage, which set a ck engine light. That's why I ended up nuying the manuals and scanner. Glad I did now, but don't know how much longer I'll be able to work on it myself.

Does yours have the 2 battery isolaters under the hood? Have you tried to charge the chassis battery?
 
92GA said:
Does yours have the 2 battery isolaters under the hood? Have you tried to charge the chassis battery?
Click to expand...
I have a mechanic on the way to look at it. I don't know what the battery isolators would look like or where they would be. I have not tried to charge the chassis battery. It appears to be functioning correctly.
 
Tom, I think you may not like Florida too much come May, June, July, and August..too hot & muggy for my own tastes, at least!  Here's hoping your mobile mechanic finds and corrects the problem so you can get on the road again soon.  Of course, if you do hang around the East Coast long enough you could always attend the GS Rally in Atlanta in October :)  we'd love to cross paths with you there!

Here's hoping the 'old girl' still has some miles left in her without taking you to the cleaners.

Linda
 
Steve & Linda said:
Tom, I think you may not like Florida too much come May, June, July, and August..too hot & muggy for my own tastes, at least! 
Click to expand...
The local people keep telling me it the same thing. I laugh at them. I am from Las Vegas, it doesn't get hot here, only medium. If I do stick around I will definitely make it to the GS rally.
 
Tom, the isolators are under the hood on the left side, they look like ford solinoids. Have him make sure they are passing power with the key in the on position.
 
Tom thought he had spotted a new class of bird. ::)...naw...that's one of our marsh skeeters. They were discussing how to carve up ole Tom before the big ones took him away from them.

I would be over to help Tom but I have food in the oven and cant get my make-up on straight. ;D
 
After visiting every auto parts store in the greater Orlando area and viewing 435 incorrect alternators we finally found the right one.

Moral of the story, we should have gone to NAPA first.
 
92GA said:
Tom, the isolators are under the hood on the left side, they look like ford solinoids. Have him make sure they are passing power with the key in the on position.
Click to expand...
One of the solenoids is hot all the time, the other one is only hot when the key is on.
 
Well the new alternator is installed but I have not yet taken it for a test drive. But I don't think the problem is solved. With the engine in neutral the voltmeter reads about 13.5 volts. When I tap on the gas pedal the voltage drops by a volt or so. But the wacky thing is that the speedometer jumps up to like 50 mph when I accelerate. Some times the check engine light flashes. I will have to drive it to make sure, but it still doesn't appear to be normal.
 
SeilerBird said:
Well the new alternator is installed but I have not yet taken it for a test drive. But I don't think the problem is solved. With the engine in neutral the voltmeter reads about 13.5 volts. When I tap on the gas pedal the voltage drops by a volt or so. But the wacky thing is that the speedometer jumps up to like 50 mph when I accelerate. Some times the check engine light flashes. I will have to drive it to make sure, but it still doesn't appear to be normal.
Click to expand...
I think you may be all the way back to a bad ground. If you have a set of jumper cables, I would attach both clamps on one end to the neg side of the chassis battery. On the other end, attach one clamp to the engine and the other clamp to the frame. This way, you are by-passing the battery cable and the grounding cable from the engine to the frame.
 
SeilerBird said:
One of the solenoids is hot all the time, the other one is only hot when the key is on.
Click to expand...
1 of those should only be hot when the aux start button is pressed, the other is hot when the key is on. Did they check your old alternator? Was it putting out ac volts instead of dc volts? Remember, the only imput for the speedo comes from the vss module. When you drove it the last time did you have your generator running? Trying to decipher where this ac voltage is leaking from. Those 2 speed sensor/generators on the trans should be the only thing left to generate ac power, but they can't generate unless the coach is moving.  Time for me to go back to the book, can't remember what all does what, heck it's been a month. Check that ground wire that goes from the left rear head to the frame, take it off and clean both ends real good.
 
You must log in or register to reply here.

Latest posts

Members online

Total: 1,032 (members: 28, guests: 1,004)

Forum statistics

Threads
131,929
Posts
1,387,676
Members
137,677
Latest member
automedicmobile
Back
Top Bottom